Exoprosthesis for the human knee joint

ABSTRACT

The present invention relates to an exoprosthesis for the human knee joint consisting of a thigh part (1) which can be connected to the human thigh as well as a lower leg part (6) which can be connected to the human lower leg or which can replace it. The lower leg part (6) and the thigh part (1) are connected through a four-bar arrangement which consists of two parallel arranged partial joints, specifically a medial joint (11) and a lateral joint (10) each of which has the joint geometry of a link chain with two articulated axles (M u , M o  ; L o , L u ) (dimer link chains). The joint geometry of the medial joint (11) is designed as an overlapping, dimer link chain in which the articulated axle M u  of the lower leg part (6) is displaced in the direction towards the thigh part (1) with respect to the articulated axle M o  of the thigh part (1) and the joint geometry of the lateral joint (10) is designed as an extended dimer chain in which the articulated axle L u  of the lower leg part (6) is displaced with respect to the articulated axle L o  of the thigh part (1) in the direction towards the lower leg (8). Both articulated axles of the lateral joint (10) and the medial joint (11) are connected with one another in an articulated manner in each case by means of a coupling link (13,14).

The present invention relates to an exoprosthesis for the human kneejoint.

The known exoprostheses for the human knee joint are multiple-jointarrangements using ball joints and/or hinge joints. Such jointarrangements, however, are not suitable for approximating the actualfunction of the human knee joint in an essentially natural manner, sothat these exoprostheses cause a considerable walking impediment.

The object of the invention is to create an exoprosthesis for the humanknee joint which has a joint function which essentially corresponds tothe natural function of the human knee joint.

According to the invention this is achieved in that the exoprosthesisconsists of a thigh part which can be connected to the human thigh aswell as a lower leg part which can be connected to the human lower legor can replace it, whereby the lower leg part and the upper leg part areconnected by a four-bar arrangement which consists of two parallelarranged partial joints and, specifically, a medial joint and a lateraljoint which in each case have the joint geometry of a link chain withtwo articulated axles (dimer joint chains), whereby the joint geometryof the medial joint is designed as an overlapping, dimer link chain inwhich the articulated axle of the lower leg part is displaced in thedirection towards the thigh part with respect to the articulated axlesof the thigh part, and the joint geometry of the lateral joint isdesigned as an extended dimer chain in which the articulated axle of thelower leg part is displaced with respect to the articulated axis of thethigh part in the direction towards the lower leg and the twoarticulated axles of the lateral joint and the medial joint each areconnected in an articulated manner to one another by means of a couplinglink. The medial joint is stable with regard to pressure due to itsjoint geometry, whereas the lateral joint is labile. By means of thedesign according to the invention, it is assured that the exoprosthesishas freedom of movement in only one joint plane and at the same timehigh mechanical stability is achieved whereby a great spectrum ofvariation is available for adaptation to individual situations.

The invention is explained in more detail on the basis of the embodimentexamples presented in the attached drawings. Shown are:

FIG. 1, a frontal view of an exoprosthesis according to the invention inthe state fastened to a human leg, cut in section,

FIG. 2, a side view according to arrow II in FIG. 1,

FIG. 3, a side view of another embodiment form of a prosthesis accordingto the invention in the state fastened to the human leg,

FIG. 4, a cut through another embodiment form of an exoprosthesisaccording to the invention as a replacement of the human knee joint,

FIG. 5, a side view of the exoprosthesis according to the inventionaccording to FIG. 4 in the direction of arrow V.

FIG. 6, a presentation in principle of the joint geometry in the sideview according to FIG. 2.

As shown in FIG. 1, a prosthesis according to the invention consists ofthigh part 1, which consists, in the presented embodiment example, oftwo thigh bars 2,2a which in each case run on the medial (inner) andlateral (outer) side of thigh 3 of human leg 4 and are connected to oneanother through cross bars 5 which encircle thigh 3. Lower leg part 6 isformed from two lower leg bars 7,7a on the medial and lateral side oflower leg 8 of leg 4 which are connected by cross bars 9 whereby crossbars 9 in turn surround lower leg 8. Lateral thigh and lower leg bars2,7 as well as medial thigh and lower leg bars 2a, 7a are connected ineach case through a double joint, specifically lateral joint 10 andmedial joint 11, which lie adjacent to one another in two parallelplanes, that is, the two parallel arranged double joints form a four-bararrangement. Lateral joint 10 and medial joint 11 have the jointgeometry of a link chain with two articulated axles, a so-called dimerlink chain. Here, lateral joint 10 is designed as an extended, dimerlink chain with the two articulated axles L_(o), L_(u), wherebyarticulated axle L_(o) is connected to articulated axle L_(u) bycoupling link 13, in an articulated manner. Articulated axles L_(o) andL_(u) have the rotation centers M₁ and M₂, and run perpendicular to thesagittal plane or perpendicular to the pivotal plane of leg 6. In theextended leg position represented, articulated axles L_(o) and L_(u) areat an interval from one another,. specifically, L_(o) displaced in thedirection towards thigh 3 and articulated axle L_(u) displaced in thedirection towards the lower leg. Coupling links 13 and 14 are arrangedparallel and vertically in the standing position.

Medial joint 11 is designed as an overlapping, dimer link chain, wherebyarticulated axle M_(u) of lower leg bar 7a is displaced in the directiontowards thigh 3 with respect to articulated axle M_(o) of thigh bar 2a,and specifically with reference to the extended leg positionrepresented. Both articulated axles M_(u) and M_(o) are connected to oneanother in an articulated manner by coupling link 14. The constructionof this arrangement is functionally realized in that both bars 2a and 7aoverlap on their ends, and in the area of overlap, coupling link 14 ismounted between bars 2a and 7a, and is connected in an articulatedmanner at one end to articulated axle M_(u) and at the other end toarticulated axle M_(o). So that the overlapping or folded, arrangementis possible, lower leg bar 7a is bent in the medial direction or thighbar 2a is bent in the lateral direction. Furthermore, it is to berecognized that articulated axle M_(o) of thigh bar 2a of medial joint11 is functionally displaced with respect to articulated axle L_(o) ofthigh bar 2 of lateral joint 10 by the displacement measure Δx in thedirection towards the thigh part. Furthermore, in the side viewaccording to FIG. 2, it can be seen that articulated axle L_(o) isfunctionally displaced with respect to articulated axle M_(o) in theposterior direction by the displacement amount Δy. In the extended dimerchain of lateral joint 10, the rotation center M₂ in L_(u) movesrelative to the rotation center M₁ in L_(o) or in the other direction ona circular path around M₁ with a radius R which corresponds to theinterval of axles L_(o) and L_(u). Here, R is the relevant length ofcoupling length 13. In the overlapping dimer chain of medial joint 11,rotation center M₃ in M_(u) moves relative to rotation center M₄ inM_(o) or in the other direction on a circular path around rotationcenter M₃ with the radius RL, which corresponds to the interval of axlesM_(u) and M_(o) which in turn represents the relative length of couplinglink 14. Regarding the above movements along a circular path, rotationsoccur around each of the rotation centers M₁ to M₄.

Whereas FIGS. 1 and 2 show how the exoprosthesis according to theinvention is designed to grip the human diseased knee bilaterally, FIG.3 shows an embodiment form in which the four-bar arrangement accordingto the invention is fastened unilaterally to the human diseased knee,for example, laterally. In this case, the same parts as in FIGS. 1 and 2are provided with the same reference numbers. The design of lateraljoint 10 corresponds to the design according to FIGS. 1 and 2. Medialjoint 11 is constructed from extension 16 on lower leg bar 7 whichoverlaps the bearing end of thigh bar 2 and, seen laterally in thedirection towards the human knee, ends behind the bearing end 2 of thighbar 2 so that lateral joint 10 and medial joint 11 are arranged parallelto one another whereby coupling link 14 of medial joint 11, also seen inthe direction towards the knee is hinged behind thigh bar 2 througharticulated axle M to its bearing tip.

In FIGS. 4 and 5, an embodiment form of an exoprosthesis is representedin which the human knee joint is completely and permanently replaced bythe latter, whereas the embodiments according to FIGS. 1 to 3 areintended only as aids, when the existing human knee is not itselfcapable of performing the normal joint function. In FIGS. 4 and 5, inturn, the same parts as in FIGS. 1 and 3 are provided with the samereference numbers. Lateral joint 10 and medial joint 11 are in this casefastened to thigh stump 20 which can be implanted and lower leg stump 21which may be part of a lower leg prosthesis. Lateral joint 10 isconstructed from bearing extension 22 designed on thigh stump 20 andbearing extension 23 designed on lower leg stump 21 which are connectedin an articulated manner through coupling link 13, for which couplinglink 13 is fastened in an articulated manner through articulated axleL_(o) to bearing extension 22 and through articulated axle L_(u) tobearing extension 23. Medial joint 11 is constructed from jointextension 25 on thigh stump 20 and joint extension 26 on lower leg stump21, whereby joint extension 26 overlaps joint extension 25 and liesbetween joint extension 25 and bearing extension 22. Coupling link 14 isarranged spatially between the two joint extensions 25,26 and isconnected in an articulated manner with the free end of joint extension26 through joint axle M_(u) and with the free end of joint extension 25through articulated axle M_(o). As evident from the representation here,a displacement of lateral joint 10 towards the posterior with respect tomedial joint 11 by the amount Δy is advantageously provided, andarticulated axle M_(o) is displaced with respect to articulated axleL_(o) by the displacement amount Δx in the direction of the thigh.

Furthermore, it is within the scope of the invention that coupling links13,14 are fastened interchangeably so that using the other prosthesisparts, the joint geometry can be changed by a change of the length ofcoupling links 13,14, and can be adapted to the specific situations ineach case. It can also be provided according to the invention that thelength of the thigh and lower leg bars is designed variably.Accordingly, the joint extensions according to FIGS. 4 and 5 can also bedesigned to be changeable with regard to their length. In addition, thebearing position of articulated axles L_(o), L_(u) and M_(u), M_(o) canbe designed so that they are mounted in a changeable manner with respectto their height or lateral bearing position.

FIG. 6 shows the geometric relationships of an exoprosthesis accordingto the invention in a side view according to FIG. 2. The two joints 10,11 are incorporated according to the invention so that their four-baraxles L_(o), L_(u) and M_(o), M_(u) run parallel to one another in twoparallel planes and that lateral joint 10 is occupied sic; displaced!with respect to medial joint 11 somewhat towards the posterior, that is,towards the back, by the measurement, Δy.

Such a joint formation represents a four-bar joint whereby the linemarked F represents the thigh part and the line marked T forms the lowerleg part. In the following examination, it is assumed that thigh part Fstands firm and forms the stand. The relative movement of the lower legwith respect to the thigh is represented as movement of part T. Sincethe length of T is greater than the sum of the lengths of coupling links13,14, articulated axle L_(o) can move only towards the posterior, awayfrom the initial position, which is marked bold. Articulated axle M_(u)can move both towards anterior as well as towards posterior. In bothcases, however, the distal extension of T, the lower leg, swingsbackwards. Both cases represent two possible bending movements of theknee, whereby each individual movement occurs automatically. In theanterior movement of articulated axle M_(u), the latter moves furthertoward the anterior after exceeding the anterior dead-center position(coupling link 14 and line T form a straight line and coincide). Thelower leg part can then assume the position a₁, indicated by thin lines.In the posterior movement of M_(u), this articulated axle reaches itsmost posterior position in the posterior dead-center position (couplinglink 13 and line T form a straight line and coincide, position b₁). As aconsequence of further movement, M_(u) then moves in the anteriordirection. This movement occurs so slowly that in this further swingingof the lower leg part, articulated axle M_(u) appears to remain at itslocation (position b₂ of T). In each case (a₁, b₁, b₂) the lower leg isswung backwards. The artificial joint is, thus, constructed so thatunder the effects of the forces actuated by pressure, the lower leg canonly swing backwards.

Since medial joint 11 is displaced in the direction towards the thighwith regard to its articulated axles M_(u) and M_(o) by the measurementΔx, through the size of this displacement, the maximum pivoting angle μmax of the joint which corresponds to the maximum bending angle of thehuman knee can be influenced towards the posterior. In this way, theregularity is established that the greater the displacement Δx, thesmaller the maximum pivoting angle μ max. Preferably, the displacementamount Δx is selected such that the connection length F from L_(o) toM_(u) describes an angle a with respect to the horizontal line which isbetween 0° and 45°: 0°<a<45°. It is also within the scope of the presentinvention that lateral joint 10 and medial joint 11 are arranged so thatthe planes through their coupling links 13,14 run spatially inclinedtowards one another from which results a spherical course of movement.

We claim:
 1. An exoprosthesis for the human knee joint comprising:athigh part (1) and a lower leg part (6); the lower leg part (6) and thethigh part (1) being mutually interconnected by a four-joint arrangementincluding a medial joint (11) and a lateral joint (10); the medial jointand the lateral joint respectively having a joint geometry of a jointchain with coupling elements (13, 14) and two joint axles (M_(u), M_(o); L_(u), L_(o)), wherein the joint geometry of the medial joint (11)forms a folded dimeric chain and the joint geometry of the lateral joint(10) forms an extended dimeric joint chain, where the joint axles (L_(o)L_(u)) of the lateral joint (10) are coupled in an articulated fashionby the coupling element (13) and the joint axles (M_(u), M_(o)) of themedial joint are coupled in an articulated fashion by the couplingelement (14); the joint axle (M_(u)) between the lower part (6) and thecoupling element (14) of the medial joint (11) being offset relative tothe joint axle (M_(o)), between the coupling element (14) and the thighpart (1), in a direction toward the thigh part (1) in an extendedposition of the knee joint; the joint axle (L_(u)) between the lower legpart (6) and the coupling element (13) of the lateral joint (10) beingconnected in an articulated fashion to the thigh part (1) at the jointaxle (L_(o)) and being offset, relative to the joint axle (L_(o)), in adirection toward the lower leg part (6); whereby in the extendedposition of the knee joint, the coupling elements (13, 14) extendparallel in two parallel planes that respectively intersect with thejoint axles of the lateral joint (L_(o), L_(u)) and the medial joint(M_(u), M_(o)); the lateral joint (10) is offset relative to the medialjoint (11) in the posterior direction by a distance (Δy) thatcorresponds to the distance between the two parallel planes; and thejoint axles (M_(u), M_(o)) of the medial joint (11) are offset relativeto the lateral joint (10) in the direction toward the thigh (3) by adistance (Δx) that corresponds to the distance between the joint axles(L_(o), M_(o).
 2. The exoprosthesis according to claim 1, wherein:thethigh part (1) comprises two thigh braces (2,2a) that extend on theinner and outer side of the thigh (3) of a human leg (4) and areconnected to one another by lateral braces (5) that encompass the thigh(3); the lower leg part (6) comprises two lower leg braces (7,7a) thatare arranged on the medial and the lateral side of the lower leg (8) ofa human leg (4); and the lower leg braces (7,7a) are connected to oneanother by lateral braces (9) that encompass the lower leg (8).
 3. Theexoprosthesis according to claim 2, wherein:the lateral joint (10) andthe medial joint (11) are collectively arranged on the lateral side ofthe human knee; the medial joint (11) is formed by an extension (16) ofthe lower leg brace (7) that overlaps a bearing end of the thigh brace(2) in the direction toward the thigh and, viewed laterally in thedirection toward the human knee, ends behind the bearing end of thethigh braces (2) such that the lateral joint (10) and the medial joint(11) by the distance (Δy); is parallel to the coupling element (14) ofthe medial joint (11), viewed in the direction toward the knee, iscoupled to the bearing end of the thigh brace behind said thigh brace bymeans of the joint axle M_(u).
 4. The exoprosthesis according to claim1, wherein:the lateral joint (10) and the medial joint (11) arerespectively fastened to a thigh stub (20) and a lower leg stub (21)that forms part of a lower leg prosthesis; the lateral joint (10) isformed by a bearing extension (22) of the thigh stub (20) and a bearingextension (23) of the lower leg stub (21); both bearing extensions areconnected to one another in articulated fashion by a coupling element(13,14); the medial joint (11) is formed by a joint extension (25) onthe thigh stub (20) and a joint extension (26) on the lower leg stub(21); the joint extension (26) overlaps the joint extension (25) andlies between the joint extension (25) and the bearing extension (22);and the coupling element (14) is arranged between the two jointextensions (25,26).